Introduced helpful messages to exception classes.

src/Exceptions/CircularReferenceException.php

@@ -4,4 +4,18 @@
 
 use Exception;
 
-class CircularReferenceException extends Exception {}
+class CircularReferenceException extends Exception
+{
+    /**
+     * Create a new exception instance.
+     *
+     * @param  string|null  $message
+     * @param  mixed|null  $code
+     * @param  \Exception|null  $previous
+     * @return void
+     */
+    public function __construct($message = null, $code = null, Exception $previous = null)
+    {
+        parent::__construct($message ?? 'This operation caused a circular reference.', $code, $previous);
+    }
+}

src/Exceptions/TooManyHopsException.php

@@ -4,4 +4,16 @@
 
 use Exception;
 
-class TooManyHopsException extends Exception {}
+class TooManyHopsException extends Exception
+{
+    /**
+     * Create a new exception instance.
+     *
+     * @param  int $maximumAllowableHops
+     * @return static
+     */
+    public static function make(int $maximumAllowableHops)
+    {
+        return new static("This operation exceeded the maximum allowable hops ({$maximumAllowableHops}).");
+    }
+}

src/Tasks/AddDagEdge.php

@@ -260,7 +260,7 @@ protected function getNewlyInsertedEdges(DagEdge $edge) : Collection
     protected function guardAgainstExceedingMaximumHops(Collection $newEdges)
     {
         if ($newEdges->isNotEmpty() && ($newEdges->last()->hops > $this->maxHops)) {
-            throw new TooManyHopsException("Maximum hops ({$this->maxHops}) exceeded");
+            throw TooManyHopsException::make($this->maxHops);
         }
     }
 }

tests/DagManagerTest.php

@@ -94,6 +94,7 @@ public function it_does_not_allow_circular_references()
          *  - the expected exception will be thrown
          */
         $this->expectException(CircularReferenceException::class);
+        $this->expectExceptionMessage('This operation caused a circular reference.');
 
         /**
          * Act/When:
@@ -495,6 +496,9 @@ public function it_cannot_exceed_max_hops($initialEdges, $lastStrawEdge)
          */
         $this->expectException(TooManyHopsException::class);
 
+        /** @todo This assertion to be replace by expectExceptionMessageMatches() from 9.0. */
+        $this->expectExceptionMessageRegExp('/This operation exceeded the maximum allowable hops \(\d\)\./');
+
         /**
          * Act/When:
          *  - insert the "last straw" edge